Re: Is OS_INFO_VMCOREINFO unimplemented?

[Petr Tesarik <ptesarik@suse.cz>]

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Hi Philipp,

On Fri, 16 Oct 2020 16:11:25 +0200
Philipp Rudo <prudo@linux.ibm.com> wrote:

> Hi Petr,
> 
> sorry for the late reply.

No problem. ;-)

> It's an interface for non-Linux systems for the stand-alone kdump.
> 
> But that's all I'm sure of. I'm afraid only Michael knows the full history
> behind the implementation. Unfortunately he left IBM ~2 years ago so this piece
> of knowledge is lost...
> 
> My theory is that originally it was planned to use this mechanism for the
> "normal" kdump as well. But for kdump common code "corrupts" the vmcoreinfo by
> adding the CRASHTIME shortly before kexec'ing the crash kernel. So the crash
> kernel would refuse to load the os_info anyway and thus it is never set.

Sure, the checksum would have to be recalculated after setting CRASHTIME. But that's perfectly possible.

> Hope this helps you at least a little

Yes, to some extent. The reason I asked was that I also implemented parsing of OS_INFO_VMCOREINFO in libkdumpfile a few years ago, but it has no test coverage. So, I looked around a bit and to my surprise all dump files contained a NULL pointer there, which looked somewhat suspicious.

Anyway, if nobody knows for certain, then my plan is to add the necessary code to the Linux kernel. Patch coming soon on the mailing list. ;-)

Thanks,
Petr T

> Philipp
> 
> 
> On Tue, 13 Oct 2020 14:53:03 +0200
> Petr Tesarik <ptesarik@suse.cz> wrote:
> 
> > Hi all,
> > 
> > I've been looking into kernel crash dump analysis for some time now,
> > and I've noticed that none of my sample dumps for z/Architecture sets
> > OS_INFO_VMCOREINFO.
> > 
> > Commit 4857d4bbe9821c8d732cb84455e18e12b3d79add suggests that the
> > "os_info" structure should contain vmcoreinfo, but it seems that the
> > corresponding fields are always zero, and a quick grep for
> > OS_INFO_VMCOREINFO finds only code that tries to read this entry in the
> > panic kernel, but no code that would initialize it in the old (crashed)
> > kernel.
> > 
> > In short, the panic kernel always prints an informational message that
> > entry 0 is not available and falls back to get_vmcoreinfo_old().
> > 
> > Is this a bug, or is this interface used by a non-Linux operating
> > system that I'm not aware of?
> > 
> > TIA,
> > Petr Tesarik
> > SUSE HW Enablement  


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